Introduction:Fine Needle Aspiration Cytology (FNAC) is considered as an independent and accurate diagnostic test for the different types of thyroid swelling. Adequacy is dependent on the technique and nature of the lesion.

Aim: To study the various cell patterns of thyroid aspiration and evaluation of the concordance between FNAC and Histopathology findings.

Materials and Methods: A prospective study was conducted during a period of September 2015 to November 2017. Correlation of FNAC and histology findings has been interpreted. FNAC of 502 patients presented with features of enlarged thyroid gland was analysed. All the relevant details about age, sex, duration of swelling and thyroid profile were taken. The diagnosis of lesions were made based on the presence of primary dominant cell pattern and included macro/normofollicular, microfollicular, papillary, syncytial, dispersed, cystic pattern and degenerated plus granulomas pattern. Total 203 specimens were examined for histology and compared with FNAC findings. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy were evaluated.

Results: A total of 502 thyroid swellings were studied, out of which, 6 cases were inadequate and revealed blood only. On the basis of primary dominant cell pattern, the macro/normofollicular pattern was noted in 189 (38.10%) cases, microfollicular pattern in 79 (15.93%) cases, papillary pattern in 18 (03.63%) cases, syncytial pattern in 80 (16.13%) cases, dispersed pattern in 33( 06.65%) cases, cystic pattern in 87 (17.54%) cases granulomas in 10 (2.02%) cases. Normo/macrofollicular (35.28%) and cystic pattern (14.51%) were common in colloid goiter which was also a common finding in FNAC (52.02%) and in histology (55.66%). In Hashimoto thyroiditis, frequent pattern noted were syncytial (13%) and dispersed (03.42%). Microfollicular (09.6%) and papillary pattern (03.62%) were common in follicular and papillary carcinoma respectively. FNAC and histology concordant were noted in 195/203 (96%) cases. 5 of 8 discordant cases were malignant and 3 /8 were benign. Overall the sensitivity, specificity, positive predictive value and negative predictive value were 93.54%, 98.59%, 98.30% and 97.91% respectively. Diagnostic accuracy of FNAC was 97.22%.

Conclusion: FNAC is a microinvasive, inexpensive and important tool for the evaluation of patients with thyroid swellings. Differential diagnosis can be encountered on the basis of various cellular patterns that can be narrowed by histopathological examination.